The present invention relates to a document conveying device and a document reading device operable therewith and, more particularly, to a document conveying device capable of conveying a document back and forth, and a document reading device for reading the image of the document by illuminating it from one edge to the other edge.
An image reading device of the type reading a document moving via an illuminating position by sequentially illuminating it from one edge to the other edge i s conventional. This type of device is often loaded with a document conveying device capable of conveying, when a single document should be read a plurality of times, the document a plurality of times via the illuminating position. The document conveying device is generally implemented by either a loop circulation system or a horizontal reciprocation system. Document conveying devices using the loop circulation system (referred to as first type of devices hereinafter) are disclosed in, for example, Japanese Patent Laid-Open Publication Nos. 60-83930 and 4-172372, Japanese Patent Publication Nos. 62-61273 and 2-16516, and Japanese Utility Model Laid-Open Publication Nos. 60-177140 and 61-194822. Document conveying devices using the horizontal circulation system (referred to as a second type of devices hereinafter) are taught in, for example, Japanese Patent Laid-Open Publication Nos. 57-83965, 59-154464, 2-129669 and 4-29543, and Japanese Utility Model Laid-Open Publication Nos. 64-43349 and 4-79844.
The problem with the first type of document conveying device is that a document of relatively large size cannot be repeatedly circulated via the glass platen unless the loop is long enough to accommodate even such a document. Such a long loop makes the device bulky and increases the number of parts and, therefore, the cost. The second type of device is free from this problem. Specifically, the second type of device causes drive rollers to convey a document horizontally in a reciprocating motion between an upstream position and a downstream position via a glass platen. However, the second type of device has the following problem. As to the first type of device, a document expected to be turned over is stacked on a document table face up and, therefore, easy to see the orientation of an image. However, with the second type of device, it is necessary to lay the document on the table face down since it is not turned over during the reciprocating motion. Hence, it is troublesome to see the orientation of an image when, for example, the leading edge of a paper should be left blank over a desired distance. Moreover, since the document fed forward is again returned to the table, another document to be scanned cannot be laid on the table beforehand. This lowers the maneuverability of the device.
The problems stated above can be obviated by a third type of document conveying device taught in Japanese Patent Laid-Open Publication No. 4-29543. Specifically, the third type of device, like the first type of device, has a document table above a glass platen and causes a turn roller 14 and a driven roller to turn over a document via a turn path. At the same time, this type of device causes the drive roller, turn roller and driven roller to convey the document P horizontally in a reciprocating motion via the glass platen. Even the third type of device has some issues yet to be solved, as follows. Since the document is turned over and then moved along the glass platen, it is driven out to a document tray located at the left-hand side of the device. A document reading device loaded with the third type of device illuminates the document being moved from the right to the left of the device, so that a photoconductive drum is rotated counterclockwise to discharge the paper to the right. Generally, therefore, a document reading device capable of reading a document having, for example, a great width is so oriented as to locate the operating section thereof at the left-hand side. Then, since the papers are driven out to the right-hand side or rear of the device, the operator cannot take them out unless stepping round to the rear of the device. This is also true with the first type of device. The second type of device allows the table and stacker to be located at the front of the device since it moves the document back and forth horizontally. However, even the second type of device forces the operator to step round to the rear of the device for taking out the document received by the tray.
The following arrangement may be contemplated in order to eliminate the above problems. In the arrangement, the third type of document conveying device is mounted on a document reading device. A paper expected to be driven out by a heat roller is redirected to a discharge roller. As a result, the discharge roller discharges the paper to the top rear side. A stacker for stacking papers is mounted on the top of the document reading device. Such a scheme will allow both the document and the papers to be collected at the front of the device. However, this cannot be done with the horizontal reciprocation system since the document is moved horizontally even to the top rear side of the device where the paper should be driven out.
The first type of device using the loop circulation system may be provided with means for correcting the skew or offset of a document in conveyance, as taught in, for example, Japanese Patent Laid-Open Publication No. 4-172372, Japanese Patent Publication No. 2-16516, or Japanese Utility Model Laid-Open Publication No. 60-177140 or 3-73551. Although the correcting means is applicable to the second or the third type of device, it is too complicated and expensive to implement an inexpensive document conveying device using the horizontal reciprocating system. As a result, the document conveyance accuracy achievable with the third type of device is low.